<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="https://cdn.jsdelivr.net/npm/vue@2.6.10/dist/vue.js"></script>
    <style>
      .list-item {
        display: inline-block;
        margin-right: 10px;
      }
  
      .list-enter-active,
      .list-leave-active {
        transition: all 1s;
      }
  
      .list-enter,
      .list-leave-to {
        opacity: 0;
        transform: translateY(30px);
      }
    </style>
  </head>
  
  <body>
    <!-- 列表的进入/离开过渡 -->
    <div id="app">
      <button @click="add">Add</button>
      <button @click="remove">Remove</button>
      <transition-group name="list" tag="p">
        <span v-for="item in items" :key="item" class="list-item">
          {{ item }}
        </span>
      </transition-group>
    </div>
    <script>
      var app = new Vue({
        el: '#app',
        data: {
          items: [1, 2, 3, 4, 5, 6, 7, 8, 9],
          nextNum: 10
        },
        methods: {
          randomIndex: function () {
            return Math.floor(Math.random() * this.items.length)
          },
          add: function () {
            this.items.splice(this.randomIndex(), 0, this.nextNum++)
          },
          remove: function () {
            this.items.splice(this.randomIndex(), 1)
          }
        }
      })
    </script>
  </body>
  
  </html>